Organic light-emitting diode display device including a thin film encapsulation layer

ABSTRACT

A display device includes: a substrate; an organic light-emitting diode positioned above the substrate; and a thin film encapsulation layer disposed on the organic light-emitting diode. The thin film encapsulation layer includes: at least one inorganic layer; and at least one organic layer disposed on the at least one inorganic layer. The at least one organic layer has a refractive index of about 1.66 or greater.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2016-0120123, filed on Sep. 20, 2016 in the KoreanIntellectual Property Office, the disclosure of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

Exemplary embodiments of the present invention relate to a displaydevice, and more particularly to an organic light-emitting diode(“OLED”) display device including a thin film encapsulation layer, thethin film encapsulation layer.

DISCUSSION OF RELATED ART

An organic light-emitting diode (“OLED”) display device may be aself-luminous display device, for example, that displays an image usingan OLED emitting light. OLED display devices may have high qualitycharacteristics such as a relatively low power consumption, a relativelyhigh luminance, and a relatively high reaction speed.

The OLED display devices may have a multi-layered structure. Themulti-layered structure may include an OLED. Due to such a structure,light emitted from the OLED may be extinguished when emitted to theoutside. Thus, the OLED display device may have a relatively lowluminous efficiency.

SUMMARY

Exemplary embodiments of the present invention provide a display device,and more particularly an organic light-emitting diode display device.The organic light-emitting diode display device may have a relativelylow light emission deviation and relatively high light emissioncharacteristics.

Exemplary embodiments of the present invention provide an organiclight-emitting diode display device includes a substrate, an organiclight-emitting diode, and a thin film encapsulation layer. The organiclight-emitting diode is positioned above the substrate. The thin filmencapsulation layer is disposed on the organic light-emitting diode. Thethin film encapsulation layer includes at least one inorganic layer andat least one organic layer. The at least one inorganic layer is disposedon the at least one inorganic layer. The at least one organic layer hasa refractive index of about 1.66 or greater.

The at least one inorganic layer and the at least one organic layer mayhave a refractive index difference of about 0.06 or less.

The at least one organic layer may have a refractive index in a range offrom about 1.66 to about 2.8.

The at least one inorganic layer may have a refractive index in a rangeof from about 1.6 to about 2.8.

The organic layer may be formed by polymerization of at least onemonomer selected from: pentabromophenyl acrylate, 2-(9H-carbazol-9-yl)ethyl methacrylate, N-vinylcarbazole, bis(methacryloylthiophenyl)sulfide or zirconium acrylate.

The organic layer may include at least one selected from:poly(3,4-ethylenedioxythiophene) (PEDOT),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD),4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA),1,3,5-tris [N,N-bis(2-methylphenyl)-amino]benzene (o-MTDAB),1,3,5-tris[N,N-bis(3-methylphenyl)-amino]benzene (m-MTDAB), 1,3,5-tris[N,N-bis (4-methylphenyl)amino]benzene (p-MTDAB),4,4′-bis[N,N-bis(3-methylphenyl)-amino]diphenylmethane (BPPM),4,4-dicarbazolyl-1,1′-biphenyl (CBP), 4,4′,4″-tris(N-carbazole)triphenylamine (TCTA),2,2′,2″-(1,3,5-benzenetolyl)tris-[1-phenyl-1H-benzoimidazol] (TPBI) or3-(4-biphenyl)-4-phenyl-5-t-butylphenyl-1,2,4-triazole (TAZ).

The at least one inorganic layer may include a first inorganic layer anda second inorganic layer. The at least one organic layer may include afirst organic layer disposed between the first inorganic layer and thesecond inorganic layer.

The organic light-emitting diode may include a first electrode, anorganic light-emitting layer, and a second electrode. The firstelectrode may be disposed on the substrate. The organic light-emittinglayer may be disposed on the first electrode. The second electrode maybe disposed on the organic light-emitting layer.

The organic light-emitting diode may include at least one of a holeinjection layer and a hole transport layer disposed between the firstelectrode and the organic light emitting layer.

The organic light-emitting diode may include at least one of an electrontransport layer and an electron injection layer disposed between theorganic light emitting layer and the second electrode.

The organic light-emitting diode display device may further include acapping layer disposed between the organic light-emitting diode and thethin film encapsulation layer.

The organic light-emitting diode display device may further include alow refractive index layer disposed between the capping layer and thethin film encapsulation layer.

The low refractive index layer may have a refractive index in a range offrom about 1.3 to about 1.4.

The low refractive index layer may include lithium fluoride (LiF).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will become moreapparent by describing in detail exemplary embodiments thereof, withreference to the accompanying drawings, in which:

FIG. 1 is a plan view illustrating an organic light-emitting diode(“OLED”) display device according to an exemplary embodiment of thepresent invention;

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1according to an exemplary embodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating resonance in an OLEDdisplay device according to an exemplary embodiment of the presentinvention;

FIG. 4 is an emission spectrum graph of an OLED display device dependingon a wavelength of emitted light according to an exemplary embodiment ofthe present invention;

FIGS. 5 and 6 are emission spectrum graphs of an OLED display devicedepending on a thickness of a first inorganic layer according to anexemplary embodiment of the present invention;

FIG. 7 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention;

FIG. 8 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention;

FIG. 9 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention; and

FIG. 10 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. In thisregard, the exemplary embodiments may have different forms and shouldnot be construed as being limited to the exemplary embodiments of thepresent invention described herein.

Like reference numerals may refer to like elements throughout thespecification and drawings.

It will be understood that although the terms “first” and “second” maybe used herein to describe various components, these components shouldnot be limited by these terms.

Sizes of elements in the drawings may be exaggerated for clarity ofdescription.

It will be understood that when a component, such as a layer, a film, aregion, or a plate, is referred to as being “on” another component, thecomponent can be directly on the other component or interveningcomponents may be present.

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to FIGS. 1 and 2.

FIG. 1 is a plan view illustrating an organic light-emitting diode(“OLED”) display device according to an exemplary embodiment of thepresent invention. FIG. 2 is a cross-sectional view taken along a lineI-I′ of FIG. 1 according to an exemplary embodiment of the presentinvention.

Referring to FIGS. 1 and 2, an OLED display device 101 according to anexemplary embodiment of the present invention may include a substrate110, a wiring unit 130, an OLED 210, and a thin film encapsulation layer300.

The substrate 110 may include an insulating material. The insulatingmaterial may include glass, quartz, ceramic, or plastic. However,exemplary embodiments of the present invention are not limited thereto.For example, the substrate 110 may include a metallic material such asstainless steel.

A buffer layer 120 may be disposed on the substrate 110. The bufferlayer 120 may include one or more layers selected from various inorganiclayers or organic layers. The buffer layer 120 may substantially reduceor prevent undesirable elements, e.g., impurity elements or moisture,from penetrating into the wiring unit 130 or the OLED 210. The bufferlayer 120 may planarize a surface therebelow. The buffer layer 120 maybe omitted.

The wiring unit 130 may be positioned above the buffer layer 120. Thewiring unit 130 may include a switching thin film transistor (“TFT”) 10,a driving TFT 20 and a capacitor 80. The wiring unit 130 may drive theOLED 210. The OLED 210 may emit light, for example, according to adriving signal received from the wiring unit 130 to display an image.

FIGS. 1 and 2 illustrate an active matrix-type organic light-emittingdiode (AMOLED) display device 101 having a 2Tr-1 Cap structure. Forexample, the 2Tr-1 Cap structure may include two TFTs, e.g., theswitching TFT 10 and the driving TFT 20, and one capacitor 80 in eachpixel; however, exemplary embodiments of the present invention are notlimited thereto. For example, the OLED display device 101 may includethree or more TFTs and two or more capacitors in each pixel. The OLEDdisplay device 101 may include additional wirings. Herein, the term“pixel” may refer to a smallest unit for displaying an image. The OLEDdisplay device 101 may display an image using a plurality of pixels.

Each pixel PX may include the switching TFT 10, the driving TFT 20, thecapacitor 80, and the OLED 210. A gate line 151, a data line 171, and acommon power line 172 may be disposed on the wiring unit 130. The gateline 151 may extend in a first direction. The data line 171 and thecommon power line 172 may each be insulated from the gate line 151. Thedata line 171 and the common power line 172 may intersect the gate line151. Each pixel PX may be defined by the gate line 151, the data line171 and the common power line 172 as a boundary; however, exemplaryembodiments of the present invention are not limited thereto. The pixelsPX may be defined by a pixel defining layer 190.

The capacitor 80 may include a pair of capacitor plates 158 and 178. Aninsulating interlayer 145 may be disposed between the pair of capacitorplates 158 and 178. In an exemplary embodiment of the present invention,the insulating interlayer 145 may be a dielectric element. A capacitanceof the capacitor 80 may be determined by electric charges accumulated inthe capacitor 80 and a voltage across the pair of capacitor plates 158and 178.

The switching TFT 10 may include a switching semiconductor layer 131, aswitching gate electrode 152, a switching source electrode 173, and aswitching drain electrode 174. The driving TFT 20 may include a drivingsemiconductor layer 132, a driving gate electrode 155, a driving sourceelectrode 176, and a driving drain electrode 177. A gate insulatinglayer 140 may be disposed on the buffer layer 110. The gate insulatinglayer 140 may insulate the switching and driving semiconductor layers131 and 132 and the switching and driving gate electrodes 152 and 155.

The switching TFT 10 may be a switching element. The switching TFT 10may select a pixel to perform light emission. The switching gateelectrode 152 may be connected to the gate line 151. The switchingsource electrode 173 may be connected to the data line 171. Theswitching drain electrode 174 may be spaced apart from the switchingsource electrode 173. The switching drain electrode 174 may be connectedto at least one of the capacitor plates 158 or 178, e.g., the capacitorplate 158.

The driving TFT 20 may apply a driving power to a first electrode 211.Thus, an organic light-emitting layer 212 of an OLED 210 in a selectedpixel may emit light. The driving gate electrode 155 may be connected tothe capacitor plate 158 connected to the switching drain electrode 174.Each of the driving source electrode 176 and the other of the capacitorplates, e.g., the capacitor plate 178, may be connected to the commonpower line 172. The driving drain electrode 177 may be connected to thefirst electrode 211 of the OLED 210, for example, through a contacthole.

The switching TFT 10 may be driven according to, for example, a gatevoltage applied to the gate line 151. The switching TFT 10 may transmita data voltage applied to the data line 171 to the driving TFT 20. Avoltage equivalent to a difference between a common voltage applied tothe driving TFT 20 from the common power line 172 and the data voltagetransmitted by (or from) the switching TFT 10 may be stored in thecapacitor 80. A current corresponding to the voltage stored in thecapacitor 80 may flow to the OLED 210 through the driving TFT 20. Thus,the OLED 210 may emit light.

A planarization layer 146 may be disposed on the insulating interlayer145. The planarization layer 146 may include an insulating material. Theplanarization layer 146 may protect the wiring unit 130. Theplanarization layer 146 and the insulating interlayer 145 may include asame material as each other.

The OLED 210 may be disposed on the planarization layer 146. The OLED210 may include a first electrode 211, the organic light-emitting layer212, and a second electrode 213. The organic light-emitting layer 212may be disposed on the first electrode 211. The second electrode 213 maybe disposed on the organic light-emitting layer 212. Holes and electronsmay be injected into the organic light-emitting layer 212 from the firstelectrode 211 and the second electrode 213, respectively. The holes andelectrons may be combined in the organic light-emitting later 212 andmay form excitons. The OLED 210 may emit light when the excitons fallfrom an excited state to a ground state.

According to an exemplary embodiment of the present invention, the firstelectrode 211 may be an anode for injecting holes. The second electrode213 may be a cathode for injecting electrons. However, exemplaryembodiments of the present invention are not limited thereto. Forexample, the first electrode 211 may be a cathode, and the secondelectrode 213 may be an anode.

According to an exemplary embodiment of the present invention, the firstelectrode 211 may be a reflective film. The second electrode 213 may bea semi-transmissive film. Accordingly, a light generated in the organiclight-emitting layer 212 may be emitted through the second electrode213. Thus, the OLED display device 101 according to an exemplaryembodiment of the present invention may have a top emission typestructure.

The first electrode 211 may have a structure in which, for example, areflective film and a transparent conductive film are sequentiallystacked. In such an exemplary embodiment of the present invention, thetransparent conductive film of the first electrode 211 may be disposedbetween the reflective film and the organic light-emitting layer 212.

The reflective film may include one or more metals selected from:magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li),chromium (Cr), copper (Cu), oraluminum (Al). The reflective film mayhave a thickness of about 200 nm or greater.

The transparent conductive film may include a transparent conductiveoxide (TCO). The TCO may include: indium tin oxide (ITO), indium zincoxide (IZO), zinc oxide (ZnO), aluminum zinc oxide (AZO), or indiumoxide (In₂O₃). The transparent conductive film may have a relativelyhigh work function. Thus, hole injection through the first electrode 211may be performed with relative ease.

The first electrode 211 may have a triple-layer structure in which atransparent conductive film, a reflective film and a transparentconductive film are sequentially stacked.

The second electrode 213 may include a semi-transmissive film. Thesemi-transmissive film may include one or more metals selected frommagnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li),chromium (Cr), copper (Cu), or aluminum (Al). The semi-transmissive filmmay have a thickness of about 200 nm or less. As the thickness of thesemi-transmissive film decreases, the transmittance of light mayincrease. As the thickness of the semi-transmissive film increases, thetransmittance of light may decrease.

The organic light-emitting layer 212 may include a single moleculeorganic material or a polymer organic material. The organiclight-emitting layer 212 may be formed by any known method using anorganic light emitting material.

The pixel defining layer 190 may have an opening. The opening of thepixel defining layer 190 may expose a portion of the first electrode211. The organic light-emitting layer 212 and the second electrode 213may be sequentially stacked on the first electrode 211 exposed by theopening. The second electrode 213 may be disposed on the pixel defininglayer 190 and the organic light emitting layer 212. The OLED 210 mayemit light, for example, from the organic light-emitting layer 212 atthe opening of the pixel defining layer 190. Thus, the pixel defininglayer 190 may define a light emission area.

The thin film encapsulation layer 300 may be disposed on the secondelectrode 213, for example, to protect the OLED 210. The thin filmencapsulation layer 300 may reduce or prevent outside air such asmoisture or oxygen from permeating into the OLED 210.

For example, the thin film encapsulation layer 300 may include at leastone inorganic layer 311 or 312 and at least one organic layer 321. Theat least one inorganic layer 311 or 312 and the at least one organiclayer 321 may be alternately disposed.

According to an exemplary embodiment of the present invention, the atleast one organic layer 321 may have a refractive index of about 1.66 orgreater. For example, the at least one organic layer 321 may have arefractive index ranging from about 1.66 to about 2.8. The at least oneinorganic layer 311 and 312 may have a refractive index ranging fromabout 1.6 to about 2.8.

The at least one inorganic layer 311 and 312 and the at least oneorganic layer 321 may have a refractive index difference of about 0.06or less. When the refractive index difference is relatively small, lightreflection at an interfacial surface between the at least one inorganiclayer 311 and 312 and the at least one organic layer 321 may be reducedor prevented. Accordingly, optical resonance in the OLED display device101 may be reduced or prevented, and a luminance deviation due tooptical resonance may be reduced or prevented. The optical resonancewill be described in more detail below.

Referring to FIG. 2, the thin film encapsulation layer 300 may includetwo inorganic layers 311 and 312 and one organic layer 321. For example,the at least one inorganic layer may include a first inorganic layer 311and a second inorganic layer 312. The at least one organic layer mayinclude a first organic layer 321. The first inorganic layer 321 may bedisposed between the first inorganic layer 311 and the second inorganiclayer 312. The at least one inorganic layer 311 and 312 may be referredto as an inorganic layer 311 and 312. The at least one organic layer 321may be referred to as an organic layer 321. However, exemplaryembodiments of the present invention are not limited to the structuredescribed with reference to FIG. 2.

According to an exemplary embodiment of the present invention, theinorganic layer 311 and 312 may have a thickness in a range of fromabout 100 nm to about 1,000 nm. The inorganic layer 311 and 312 mayinclude at least one of silver, metal oxide, metal oxynitride, siliconoxide, silicon nitride, or silicon oxynitride. The inorganic layer 311and 312 may have substantially a same refractive index as each other.The inorganic layers 311 and 312 may have substantially a same thicknessas each other. The inorganic layers 311 and 312 may include a samematerial as each other.

For example, the inorganic layer 311 and 312 may include one or moreinorganic materials of: Al_(x)O_(y), TiO_(x), ZrO_(x), SiO_(x),AlO_(x)N_(y), Al_(x)N_(y), SiO_(x)N_(y), Si_(x)N_(y), ZnO_(x) orTa_(x)O_(y). For example, the inorganic layer 311 and 312 may includeone or more inorganic materials of: Al₂O₃, TiO₂, ZrO, SiO₂, AlON, AlN,SiON, Si₃N₄, ZnO or Ta₂O. The inorganic layer 311 and 312 may be formedthrough methods such as a chemical vapor deposition (CVD) method or anatomic layer deposition (ALD) method. However, exemplary embodiments ofthe present invention are not limited thereto. For example, theinorganic layer 311 and 312 may be formed through various methods.

The organic layer 321 may have a thickness in a range of from about 100nm to about 8,000 nm. According to an exemplary embodiment of thepresent invention, the organic layer 321 may include an organic materialhaving a relatively high refractive index. For example, the organiclayer 321 may include a polymer material having a relatively highrefractive index.

According to an exemplary embodiment of the present invention, theorganic layer 321 may be formed by polymerization of at least onemonomer selected from the following Chemical Formulae 1, 2, 3, 4 and 5.

Thus, the organic layer 321 may be formed by polymerization of at leastone monomer selected from: pentabromophenyl acrylate,2-(9H-carbazol-9-yl) ethyl methacrylate, N-vinylcarbazole, bis(methacryloylthiophenyl) sulfide or zirconium acrylate.

For example, the organic layer 321 may be formed by depositing, on theinorganic layer 311 or 312, at least one monomer selected from:pentabromophenyl acrylate, 2-(9H-carbazol-9-yl) ethyl methacrylate,N-vinylcarbazole, bis (methacryloylthiophenyl) sulfide or zirconiumacrylate.

The organic layer 321 including pentabromophenyl acrylate represented byChemical Formula 1 may have a refractive index of about 1.7.

The organic layer 321 including 2-(9H-carbazol-9-yl) ethyl methacrylaterepresented by Chemical Formula 2 may have a refractive index of about1.69.

The organic layer 321 including N-vinylcarbazole represented by ChemicalFormula 3 may have a refractive index of about 1.68.

The organic layer 321 including bis (methacryloylthiophenyl) sulfiderepresented by Chemical Formula 4 may have a refractive index of about1.66.

The organic layer 321 including zirconium acrylate represented byChemical Formula 5 may have a refractive index of about 1.66. Therefractive index of the organic layer 321 may be adjusted, for example,by adjusting the content of zirconium (Zr).

The organic layer 321 may include an acrylic resin, an epoxy resin,polyimide or polyethylene, which are polymer-based materials. Forexample, according to an exemplary embodiment of the present invention,the organic layer 321 may include at least one selected from:poly(3,4-ethylenedioxythiophene) (PEDOT),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD),4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA),1,3,5-tris [N,N-bis(2-methylphenyl)-amino]benzene (o-MTDAB),1,3,5-tris[N,N-bis(3-methylphenyl)-amino]benzene (m-MTDAB),1,3,5-tris[N,N-bis (4-methylphenyl)amino]benzene (p-MTDAB),4,4′-bis[N,N-bis(3-methylphenyl)-amino]diphenylmethane (BPPM),4,4-dicarbazolyl-1,1′-biphenyl (CBP), 4,4′,4″-tris(N-carbazole)triphenylamine (TCTA),2,2′,2″-(1,3,5-benzenetolyl)tris-[1-phenyl-1H-benzoimidazol] (TPBI) or3-(4-biphenyl)-4-phenyl-5-t-butylphenyl-1,2,4-triazole (TAZ).

The organic layer 321 may be formed, for example, through a thermaldeposition process. The thermal deposition process may be performedwithin a temperature range that does not damage the OLED 210. However,exemplary embodiments of the present invention are not limited thereto.For example, the organic layer 321 may be formed through variousmethods.

The inorganic layer 311 or 312 may have a relatively high density ofthin film. Thus, the inorganic layer 311 or 312 may substantially reduceor prevent permeation of, for example, moisture or oxygen. Permeation ofmoisture and oxygen into the OLED 210 may be reduced or prevented by theinorganic layer 311 or 312.

Moisture and oxygen that have passed through the inorganic layer 311 or312 may be substantially blocked by the organic layer 321. The organiclayer 321 may have a relatively low moisture-infiltration preventingefficacy, as compared to the inorganic layer 311 and 312. However, theorganic layer 321 may be a buffer layer. Thus, the organic layer 321 mayreduce stress among respective ones of the inorganic layer 311 and 312.The organic layer 321 may also have a moisture-infiltration preventingfunction. Further, since the organic layer 321 may have planarizationcharacteristics, an uppermost surface of the thin film encapsulationlayer 300 may be planarized by the organic layer 321.

The thin film encapsulation layer 300 may have a thickness of about 50Lm or less, e.g., about 10 m or less. Accordingly, the OLED displaydevice 101 may have a relatively small thickness. Thus, the OLED displaydevice 101 may have a relatively high flexibility.

FIG. 3 is a cross-sectional view illustrating resonance in an OLEDdisplay device according to an exemplary embodiment of the presentinvention. Referring to FIG. 3, an intermediate layer 330 may bedisposed between the OLED 210 and the thin film encapsulation layer 300.The intermediate layer 330 may include a light-transmitting material.The intermediate layer 330 may have a single-layered structure.Alternatively, the intermediate layer 330 may have a multi-layeredstructure in which a plurality of layers are stacked. The intermediatelayer 330 may be omitted.

The OLED display device S1 may have a multi-layered structure. A lightemitted from the organic light-emitting layer 212 may be emitted throughthe multi-layered structure of the OLED display device S1.

When a refractive index difference between the organic layer 321 and theinorganic layer 311 or 312 included in the thin film encapsulation layer300 is relatively large, light may be reflected at an interfacialsurface between the organic layer 321 and the inorganic layer 311 or312. Accordingly, optical resonance may be induced by the lightreflection.

Optical resonance may be referred to herein as “resonance.” Theresonance will be described with respect to the organic layer 321 andthe first inorganic layer 311, which may be one of the inorganic layers311 and 312 positioned closest to the OLED 210.

For example, referring to FIG. 3, the first inorganic layer 311 may havea refractive index of about 1.75. The organic layer 321 may have arefractive index of about 1.5.

When the first inorganic layer 311 has a refractive index of about 1.75and the organic layer 321 has a refractive index of about 1.5, arefractive index difference between the first inorganic layer 311 andthe organic layer 321 may be about 0.25. In such an exemplary embodimentof the present invention, an interfacial surface 311 a between the firstinorganic layer 311 and the organic layer 321 may be a reflectivesurface. The first electrode 211 of the top emission type OLED displaydevice may be a reflective electrode. Accordingly, light may bereflected off a surface 211 a of the first electrode 211.

When light repeats reflection between two reflective surfaces, opticalresonance may occur. When optical resonance occurs, light energy mayincrease. The light having the increased energy may relatively readilypass through the multi-layered stacked structure of the OLED displaydevice S1 to be emitted outwards. A structure allowing light resonancebetween two reflective layers may be referred to as a resonancestructure. A distance between the two reflective layers between whichresonance occurs may be referred to as a resonance distance. Theresonance distance may vary, for example, based on the wavelength oflight.

For example, when a wavelength of light emitted from the organiclight-emitting layer 212 is “λ1” and a distance between the surface 211a of the first electrode 211 and the interfacial surface 311 a betweenthe first inorganic layer 311 and the organic layer 321 is “d1,” lightresonance may occur when the following Formula 1 is satisfied.d1=m1·λ1  [Formula 1]

In Formula 1, “m1” is a natural number.

According to an exemplary embodiment of the present invention, the firstinorganic layer 311 may be formed through methods such as a chemicalvapor deposition (CVD) method or an atomic layer deposition (ALD)method. In such an exemplary embodiment of the present invention, due toprocess errors, a layer thickness may vary. Thus, a layer thickness mayvary, for example, based on the position in a single first inorganiclayer 311.

When the layer thickness of the first inorganic layer 311 varies, adistance between the surface 211 a of the first electrode 211 and theinterfacial surface 311 a between the first inorganic layer 311 and theorganic layer 321 may vary. Thus, the wavelength of light resonatedbetween the surface 211 a of the first electrode 211 and the interfacialsurface 311 a between the first inorganic layer 311 and the organiclayer 321 may vary.

FIG. 4 is an emission spectrum graph of an OLED display device accordingto the wavelength according to an exemplary embodiment of the presentinvention. In FIG. 4, C1 (represented by a dotted line) may refer to arelative luminous intensity based on the wavelength of light when thethickness of the first inorganic layer 311 is about 1 μm. C2(represented by a bold line) may refer to a relative luminous intensitybased on the wavelength of light when the thickness of the firstinorganic layer 311 is about 1.05 μm. Referring to FIG. 4, although thethickness of the first inorganic layer 311 may be changed by about 0.05μm (i.e., about 50 nm), the luminous intensity based on the wavelengthof light may vary.

The OLED display device may include a plurality of pixels. Due toprocess errors, the first inorganic layer 311 on the OLED 210 may havedifferent thicknesses corresponding to respective pixels. For example,when the thickness of the first inorganic layer 311 on red OLEDs R isnot uniform, luminous intensity of a red color may vary corresponding toeach pixel, which may be similar to a green pixel and a blue pixel.

FIG. 5 is an emission spectrum graph of an OLED display device accordingto the thickness of the first inorganic layer according to an exemplaryembodiment of the present invention. Referring to FIG. 5, as thethickness of the first inorganic layer 311 varies, luminous intensitiesof a red color R, a green color G, and a blue color B may vary.

As such, in the case where the interfacial surface 311 a between thefirst inorganic layer 311 and the organic layer 321 is a reflectivelayer, when the thickness of the first inorganic layer 311 varies, thewavelength of light resonated between the surface 211 a of the firstelectrode 211 and the interfacial surface 311 a between the firstinorganic layer 311 and the organic layer 321 may vary. In such anexemplary embodiment of the present invention, a limit in forming auniform thickness of the first inorganic layer 311 in a process ofmanufacturing the first inorganic layer 311 and the thickness of thefirst inorganic layer 311 may vary based on the position due to processerrors. Accordingly, pixels representing a same color may exhibitdifferent luminous intensities based on the position.

According to an exemplary embodiment of the present invention, at leastthe organic layer 321 may have a refractive index of about 1.66 or more.For example, the organic layer 321 may have a refractive index in arange of from about 1.66 to about 2.8. Accordingly, a refractive indexdifference between the inorganic layer 311 or 312 and the organic layer321 may be reduced to about 0.06 or less. Thus, light reflection at theinterfacial surface between the inorganic layer 311 and 312 and theorganic layer 321 may be reduced or prevented.

According to an exemplary embodiment of the present invention, arefractive index difference between the first inorganic layer 311 andthe organic layer 321 may be relatively small since the organic layer321 may include a relatively high refractive index material and may havea relatively large refractive index of about 1.66 or more. Thus, thefirst inorganic layer 311 and the organic layer 321 may have arefractive index difference of about 0.06 or less. The first inorganiclayer 311 and the organic layer 321 may have substantially a samerefractive index as each other (e.g., the refractive indexdifference=0). Thus, light might not be reflected between the firstinorganic layer 311 and the organic layer 321. Accordingly, even if thethickness of the first inorganic layer 311 varies depending on theposition due to process errors, there may be substantially no deviationin luminous efficiency due to resonance of light. Even if there is adeviation in the thickness of the first inorganic layer 311, there is nodeviation in the luminous intensity.

Accordingly, the OLED display device 101 according to an exemplaryembodiment of the present invention may have a substantially uniformluminous efficiency for each pixel or position.

FIG. 6 is an emission spectrum graph of an OLED display device accordingto the thickness of the first inorganic layer according to an exemplaryembodiment of the present invention. The OLED display device may referto the OLED display device 101 according to an exemplary embodiment ofthe present invention.

Referring to FIG. 6, even if the thickness of the first inorganic layer311 varies, luminous intensities of a red pixel R, a green pixel G and ablue pixel B might not substantially vary. Thus, there may be nosubstantial deviation in luminous intensity depending on the thicknessof the first inorganic layer 311.

An exemplary embodiment of the present invention will be described inmore detail below with reference to FIG. 7.

FIG. 7 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention.Descriptions of the above-described components may be omitted below.

The OLED display device 102 according to an exemplary embodiment of thepresent invention may include a first light emission auxiliary layer215. The first light emission auxiliary layer 215 may be disposedbetween a first electrode 211 and an organic light-emitting layer 212.The first light emission auxiliary layer 215 may include at least one ofa hole injection layer HIL and a hole transport layer HTL. The firstlight emission auxiliary layer 215 may include the hole injection layerand the hole transport layer.

The OLED display device 102 according to an exemplary embodiment of thepresent invention may include a second light emission auxiliary layer217. The second light emission auxiliary layer 217 may be disposedbetween the organic light emitting layer 212 and a second electrode 213.The second light emission auxiliary layer 217 may include at least oneof an electron transport layer ETL and an electron injection layer EIL.The second light emission auxiliary layer 217 may include the electroninjection layer EIL and the electron transport layer ETL.

The first light emission auxiliary layer 215 and the second lightemission auxiliary layer 217 may each extend between a pixel defininglayer 190 and the second electrode 213.

The organic light-emitting layer 212, the hole injection layer, the holetransport layer, the electron transport layer and the electron injectionlayer may also be referred to as an organic layer. The organic layer mayinclude a relatively low molecular weight organic material or arelatively high molecular weight organic material.

The OLED display device 102 according to an exemplary embodiment of thepresent invention may include the first light emission auxiliary layer215 or the second light emission auxiliary layer 217. Alternatively, theOLED display device 102 may include the first light emission auxiliarylayer 215 and the second light emission auxiliary layer 217.

An exemplary embodiment of the present invention will be described inmore detail below with reference to FIG. 8.

FIG. 8 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention.

The OLED display device 103 according to an exemplary embodiment of thepresent invention may include a capping layer 230. The capping layer 230may be disposed between an OLED 210 and a thin film encapsulation layer300. Referring to FIG. 8, the capping layer 230 may be disposed betweena second electrode 213 and a first inorganic layer 311.

The capping layer 230 may have optical transparency. The capping layer230 may protect the OLED 210. The capping layer 230 may provide a lightemitted from an organic light-emitting layer 212 to be emitted to theoutside.

The capping layer 230 may include at least one of an inorganic materialand an organic material having light transmittance. Thus, the cappinglayer 230 may include an inorganic layer or an organic layer.Alternatively, the capping layer 230 may include an organic layerincluding inorganic particles.

The capping layer 230 may include two or more materials having differentrefractive indices. For example, the capping layer 230 may be formed byusing a mixture of a relatively high refractive index material and arelatively low refractive index material. The relatively high refractiveindex material and the relatively low refractive index material may bean organic material or an inorganic material, respectively.

The capping layer 230 may have a thickness in a range of from about 30nm to about 300 nm. Alternatively, the capping layer 230 may have athickness of about 300 nm or more. As the thickness of the capping layer230 increases, protection of the OLED 210 may increase. However, if thecapping layer 230 is relatively thick, a thickness of the OLED displaydevice 103 may be increased.

The capping layer 230 may be prepared by various methods. For example,the capping layer 230 may be formed by a deposition process. In thedeposition process, a relatively high refractive index material and arelatively low refractive index material may be used together. Adeposition amount or a deposition ratio of the relatively highrefractive index material and the relatively low refractive indexmaterial may be adjusted, for example, to adjust a refractive index ofthe capping layer 230. The capping layer 230 may have a refractive indexin a range of from about 1.3 to about 1.4. For example, the cappinglayer 230 may have a refractive index in a range of from about 1.35 toabout 1.38. For example, the capping layer 230 may have a refractiveindex of about 1.36.

FIG. 9 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention.

The OLED display device 104 according to an exemplary embodiment of thepresent invention may include a capping layer 230 and a low refractiveindex layer 240. The capping layer 230 and the low refractive indexlayer 240 may be sequentially disposed between an OLED 210 and a firstinorganic layer 311.

The low refractive index layer 240 may have a refractive index in arange of from about 1.3 to about 1.4. The low refractive index layer 240may have a refractive index, for example, in a range of about 1.35 toabout 1.39. For example, the low refractive index layer 240 may have arefractive index of about 1.37. The low refractive index layer 240 mayprovide a light emitted from the organic light-emitting layer 212 to beemitted to the outside.

The low refractive index layer 240 may include lithium fluoride (LiF).

FIG. 10 is a cross-sectional view illustrating an OLED display deviceaccording to an exemplary embodiment of the present invention.

According to an exemplary embodiment of the present invention, a thinfilm encapsulation layer 300 may include a plurality of inorganic layers311, 312 and 313 and a plurality of organic layers 321 and 322.

For example, the thin film encapsulation layer 300 described withreference to FIG. 10 includes three inorganic layers 311, 312 and 313and two organic layers 321 and 322. The two organic layers 321 and 322may be alternately arranged with the three inorganic layers 311, 312 and313.

The three inorganic layers 311, 312 and 313 may be a first inorganiclayer 311, a second inorganic layer 312 and a third inorganic layer 313,respectively. The two organic layers 321 and 322 may be named as a firstorganic layer 321 and a second organic layer 322, respectively.

In one or more exemplary embodiments of the present invention, the thinfilm encapsulation layer of the OLED display device may include anorganic layer having a relatively high refractive index. Accordingly, arefractive index difference between the organic layer and the inorganiclayer included in the thin film encapsulation layer may be reduced, andthe light emission characteristics of the OLED display device mayincrease.

While the present invention has been illustrated and described withreference to the exemplary embodiments thereof, it will be apparent tothose of ordinary skill in the art that various changes in form anddetail may be made thereto without departing from the spirit and scopeof the present invention.

What is claimed is:
 1. A display device, comprising: a substrate; anorganic light-emitting diode positioned above the substrate; a thin filmencapsulation layer disposed on the organic light-emitting diode; and acapping layer disposed between the organic light-emitting diode and thethin film encapsulation layer, wherein the capping layer has arefractive index in a range from about 1.3 to about 1.4; wherein thethin film encapsulation layer comprises: at least one inorganic layer;and at least one organic layer disposed on the at least one inorganiclayer, wherein the at least one organic layer has a refractive index ofabout 1.66 or greater.
 2. The display device of claim 1, wherein the atleast one inorganic layer and the at least one organic layer have arefractive index difference of about 0.06 or less.
 3. The display deviceof claim 1, wherein the at least one organic layer has a refractiveindex in a range of from about 1.66 to about 2.8.
 4. The display deviceof claim 1, wherein the at least one inorganic layer has a refractiveindex in a range of from about 1.6 to about 2.8.
 5. The display deviceof claim 1, wherein the at least one organic layer is formed bypolymerization of at least one monomer selected from: pentabromophenylacrylate, 2-(9H-carbazol-9-yl) ethyl methacrylate, N-vinylcarbazole, bis(methacryloylthiophenyl) sulfide or zirconium acrylate.
 6. The displaydevice of claim 1, wherein the at least one organic layer comprises atleast one of: poly(3,4-ethylenedioxythiophene) (PEDOT),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD),4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA),1,3,5-tris [N,N-bis(2-methylphenyl)-amino]benzene (o-MTDAB),1,3,5-tris[N,N-bis(3-methylphenyl)-amino]benzene (m-MTDAB), 1,3,5-tris[N,N-bis(4-methylphenyl)amino]benzene (p-MTDAB),4,4′-bis[N,N-bis(3-methylphenyl)-amino]diphenylmethane (BPPM),4,4-dicarbazolyl-1,1′-biphenyl (CBP), 4,4′,4″-tris(N-carbazole)triphenylamine (TCTA),2,2′,2″-(1,3,5-benzenetolyl)tris-[1-phenyl-1H-benzoimidazol] (TPBI) or3-(4-biphenyl)-4-phenyl-5-t-butylphenyl-1,2,4-triazole (TAZ).
 7. Thedisplay device of claim 1, wherein the at least one inorganic layercomprises a first inorganic layer and a second inorganic layer, and theat least one organic layer comprises a first organic layer disposedbetween the first inorganic layer and the second inorganic layer.
 8. Thedisplay device of claim 1, wherein the organic light-emitting diodecomprises: a first electrode disposed on the substrate; an organiclight-emitting layer disposed on the first electrode; and a secondelectrode disposed on the organic light-emitting layer.
 9. The displaydevice of claim 8, wherein the organic light-emitting diode comprises atleast one of a hole injection layer and a hole transport layer disposedbetween the first electrode and the organic light-emitting layer. 10.The display device of claim 8, wherein the organic light-emitting diodecomprises at least one of an electron transport layer and an electroninjection layer disposed between the organic light-emitting layer andthe second electrode.
 11. The display device of claim 1, furthercomprising a low refractive index layer disposed between the cappinglayer and the thin film encapsulation layer.
 12. The display device ofclaim 11, wherein the low refractive index layer has a refractive indexin a range of from about 1.3 to about 1.4.
 13. The display device ofclaim 11, wherein the low refractive index layer comprises lithiumfluoride (LiF).
 14. A display device, comprising: a substrate; anorganic light-emitting diode positioned above the substrate; a thin filmencapsulation layer disposed on the organic light-emitting diode; and afirst light emission auxiliary layer positioned above the substrate,wherein the organic light-emitting diode comprises: a first electrodedisposed on the substrate; and an organic light-emitting layer disposedon the first electrode, wherein the thin film encapsulation layercomprises: at least one inorganic layer; and at least one organic layerdisposed on the at least one inorganic layer, wherein the at least oneorganic layer has a refractive index of about 1.66 or greater, andwherein the first light emission auxiliary layer is disposed between thefirst electrode and the organic light-emitting layer.
 15. The displaydevice of claim 14, wherein the organic light-emitting layer furthercomprises a second electrode disposed on the organic light-emittinglayer.
 16. The display device of claim 15, wherein the display devicefurther comprises a second light emission auxiliary layer disposedbetween the organic light-emitting layer and the second electrode.
 17. Adisplay device, comprising: a substrate; an organic light-emitting diodepositioned above the substrate: a thin film encapsulation layer diposedon the organic light-emitting diode; a capping layer disposed betweenthe organic light-emitting diode and the thin film encapsulation layer,wherein the capping layer has a refractive index in a range from about1.3 to 1.4; a low refractive index layer disposed between the cappinglayer and the thin film encapsulation layer, wherein the thin filmencapsulation layer comprises: at least two inorganic layers; and atleast two organic layers alternatingly disposed with the at least twoinorganic layers, wherein the at least two organic layer have arefractive index of about 1.66 or greater.
 18. The display device ofclaim 17, wherein the at least two inorganic layers and the at least twoorganic layers have a refractive index difference of about 0.06 or less.19. The display device of claim 17, wherein the low refractive indexlayer has a refractive index in a range of from about 1.3 to about 1.4.